Differential landscape evolution in the Himalayan Piedmont zone across Kopili Fault Zone, NE India from InSAR, geomorphic and sedimentological analysis

The seismically active NNW-SSE-trending Kopili Fault Zone (KFZ), a transverse basement fault buried beneath thick Brahmaputra alluvium, partitions deformation across the southern part of the Himalaya in NE India. The northern segment of the KFZ in the Himalayan Piedmont zone experienced an Mw 6.0 earthquake in 2021, with a dominant reverse-fault component that produced extensive coseismic liquefaction in the epicentral area. The time-series Interferometric Synthetic Aperture Radar (InSAR) analysis suggests a 5–10 mm/yr uplift rate in the epicentral area during the 2017–2021 period in the eastern block of the KFZ. The time-lapse Normalized Difference Water Index (NDWI) from Landsat images over the past 40 years reveals an eastward deflection of channels. The tectonic-geomorphic proxies, such as mountain front sinuosity (Smf), normalized steepness index ( k sn ), river sinuosity, and drainage deflection, combined with sedimentation patterns and OSL dating of younger terraces, suggest differential uplift in the eastern block of the KFZ over the past millennia. These geomorphic expressions and sedimentological evidence are discussed to elucidate neotectonic growth along the northern high-angle reverse-fault segment of the KFZ and to highlight its heterogeneity.